diff --git a/.github/workflows/expat_config_h.yml b/.github/workflows/expat_config_h.yml
new file mode 100644
index 00000000..393ca36f
--- /dev/null
+++ b/.github/workflows/expat_config_h.yml
@@ -0,0 +1,30 @@
+# Copyright (C) 2020 Sebastian Pipping <sebastian@pipping.org>
+# Licensed under the MIT license
+
+name: Check expat_config.h.{in,cmake} for regressions
+
+on:
+- pull_request
+- push
+
+jobs:
+  checks:
+    name: Check expat_config.h.{in,cmake} for regressions
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2.3.4
+    - name: Check expat_config.h.{in,cmake} for regressions
+      run: |
+        set -v
+        # A non-empty diff indicates a change in the list of macros exported:
+        # - Removals would be trouble (because expat_config.h is installed).
+        # - Additions could use an extra check by a human
+        ( cd expat && ./buildconf.sh )  # generate expat_config.h.in
+        diff -u <(sort < ci_expat_config_h/expat_config_h_in__expected.txt) <(./ci_expat_config_h/list_exported_macros.sh expat/expat_config.h.in)
+        diff -u <(sort < ci_expat_config_h/expat_config_h_cmake__expected.txt) <(./ci_expat_config_h/list_exported_macros.sh expat/expat_config.h.cmake)
+
+        # Informational (and not an ideal state)
+        diff -u \
+            <(sort < ci_expat_config_h/expat_config_h_in__expected.txt) \
+            <(sort < ci_expat_config_h/expat_config_h_cmake__expected.txt) \
+            || true
diff --git a/ci_expat_config_h/expat_config_h_cmake__expected.txt b/ci_expat_config_h/expat_config_h_cmake__expected.txt
new file mode 100644
index 00000000..036948ce
--- /dev/null
+++ b/ci_expat_config_h/expat_config_h_cmake__expected.txt
@@ -0,0 +1,36 @@
+BYTEORDER
+__func__
+HAVE_ARC4RANDOM
+HAVE_ARC4RANDOM_BUF
+HAVE_DLFCN_H
+HAVE_FCNTL_H
+HAVE_GETPAGESIZE
+HAVE_GETRANDOM
+HAVE_INTTYPES_H
+HAVE_LIBBSD
+HAVE_MEMORY_H
+HAVE_MMAP
+HAVE_STDINT_H
+HAVE_STDLIB_H
+HAVE_STRING_H
+HAVE_STRINGS_H
+HAVE_SYSCALL_GETRANDOM
+HAVE_SYS_STAT_H
+HAVE_SYS_TYPES_H
+HAVE_UNISTD_H
+off_t
+PACKAGE
+PACKAGE_BUGREPORT
+PACKAGE_NAME
+PACKAGE_STRING
+PACKAGE_TARNAME
+PACKAGE_URL
+PACKAGE_VERSION
+size_t
+STDC_HEADERS
+WORDS_BIGENDIAN
+XML_ATTR_INFO
+XML_CONTEXT_BYTES
+XML_DEV_URANDOM
+XML_DTD
+XML_NS
diff --git a/ci_expat_config_h/expat_config_h_in__expected.txt b/ci_expat_config_h/expat_config_h_in__expected.txt
new file mode 100644
index 00000000..3c23e8fc
--- /dev/null
+++ b/ci_expat_config_h/expat_config_h_in__expected.txt
@@ -0,0 +1,40 @@
+AC_APPLE_UNIVERSAL_BUILD
+BYTEORDER
+const
+HAVE_ARC4RANDOM
+HAVE_ARC4RANDOM_BUF
+HAVE_DLFCN_H
+HAVE_FCNTL_H
+HAVE_GETPAGESIZE
+HAVE_GETRANDOM
+HAVE_INTTYPES_H
+HAVE_LIBBSD
+HAVE_MEMORY_H
+HAVE_MMAP
+HAVE_STDINT_H
+HAVE_STDLIB_H
+HAVE_STRING_H
+HAVE_STRINGS_H
+HAVE_SYSCALL_GETRANDOM
+HAVE_SYS_PARAM_H
+HAVE_SYS_STAT_H
+HAVE_SYS_TYPES_H
+HAVE_UNISTD_H
+LT_OBJDIR
+off_t
+PACKAGE
+PACKAGE_BUGREPORT
+PACKAGE_NAME
+PACKAGE_STRING
+PACKAGE_TARNAME
+PACKAGE_URL
+PACKAGE_VERSION
+size_t
+STDC_HEADERS
+VERSION
+WORDS_BIGENDIAN
+XML_ATTR_INFO
+XML_CONTEXT_BYTES
+XML_DEV_URANDOM
+XML_DTD
+XML_NS
diff --git a/ci_expat_config_h/list_exported_macros.sh b/ci_expat_config_h/list_exported_macros.sh
new file mode 100755
index 00000000..ee9d50b5
--- /dev/null
+++ b/ci_expat_config_h/list_exported_macros.sh
@@ -0,0 +1,2 @@
+#! /usr/bin/env bash
+grep -Eo '(define|undef) [a-zA-Z0-9_]+' "${1}" | awk '{print $2}' | sort -u
diff --git a/expat/configure.ac b/expat/configure.ac
index 82ec1fdd..71194eaa 100644
--- a/expat/configure.ac
+++ b/expat/configure.ac
@@ -105,9 +105,6 @@ EXPATCFG_COMPILER_SUPPORTS_VISIBILITY([
   AX_APPEND_FLAG([-fvisibility=hidden],       [AM_CFLAGS])
   AX_APPEND_FLAG([-DXML_ENABLE_VISIBILITY=1], [AM_CPPFLAGS])])
 
-dnl Checks for header files.
-AC_HEADER_STDC
-
 dnl Checks for typedefs, structures, and compiler characteristics.
 
 dnl We define BYTEORDER to 1234 when the platform is little endian; it